The present invention generally relates to signaling methods, switching systems, storage mediums and networks, and more particularly to a signaling method, a switching system, a storage medium and a network which are applied to communications using a signaling protocol.
Much attention is drawn to the Broadband Integrated Services Digital Network (B-ISDN) using Asynchronous Transfer Mode (ATM) as a switching technique which integrates information such as data, voice and image. Two connection types, namely, a Permanent Virtual Channel (PVC) and a Switched Virtual Channel (SVC), are prepared for the B-ISDN. The PVC does not use a signaling protocol, and conditions related to the connection, such as the connection identifier and band, are all input. On the other hand, the SVC operates a signaling protocol between nodes so as to set a connection between end systems, and a required band may be requested when required. However, depending on a service quality request such as the band and delay, a support protocol of the other party to be connected, and the like, there is a possibility that the SVC cannot make the connection. For this reason, when the signaling protocol is applied to the ATM-Local Area Network (ATM-LAN) and the connection cannot be made, the undesirable effects caused thereby are large.
Conventionally, the LAN uses a shared media and transmits data within the same segment, and provides a connectionless type communication which has no concept of connection. For this reason, in the LAN-ATM-LAN connection using the SVC, it takes time to establish the connection in the ATM and thereby affects the transfer of the data generated in the LAN to the ATM connection.
Normally, the connection type communication using the signaling protocol uses a signaling protocol prescribed by an international standardization organization such as the International Telecommunication Union-Telecommunication Standardization Sector (ITU-T) and the ATM Forum, and the transmission of the user data becomes possible only after the connection between the end systems is established. The signaling protocol prescribes the messages, procedure and the like exchanged between the end systems, and new messages and information elements may be added in order to expand the functions. On the other hand, certain information may be deleted and the procedure may be modified in the signaling protocol. In addition, in order to make the standard flexible, a portion of the message and the procedure may be prescribed as being optional, and the operation at the time of receiving the message may be by way of implementation.
A description will be given of a general connection establishing procedure of a conventional point-to-point communication for a case where connection establishment is successful, by referring to FIG. 1. This procedure is based on a standard decided by the international standardization organization. The exchange of the messages described hereunder are made using the connection for the signaling message. It is assumed that an ATM End System (AES) 101 receives a frame from the LAN, and transfers this frame to an AES 104 at the receiving end. This procedure is realized by the following steps (S1) through (S6).
(S1) The AES 101 transmits a call setup message SETUP to an ATM switching system 102 via a User Network Interface (UNI) A. This message SETUP includes a band requested by the AES 101, a Quality of Service (QoS) and the like.
(S2) The ATM switching system 102 which receives the message SETUP from the UNI A reserves a Virtual Path Identifier (VPI) or a Virtual Channel Identifier (VCI) which is a connection identifier used in the UNI A if the ATM switching system 102 can accept the message SETUP, that is, if the ATM switching system 102 can provide the conditions included in the message SETUP. A connect message CONNECT is used to notify the connection identifier to the AES 101. In addition, the ATM switching system 102 transfers the message SETUP to an adjacent ATM switching system 103 via a Network Node Interface (NNI).
(S3) The ATM switching system 103 which receives the message SETUP from the ATM switching system 102 allocates a connection identifier used in a UNI B and transmits the message SETUP including this connection identifier to the AES 104 if the ATM switching system 103 can accept the message SETUP, similarly to the ATM switching system 102.
(S4) The AES 104 which receives the message SETUP from the ATM switching system 103 responds by a message CONNECT with respect to the AES 101 if the AES 104 can accept the message SETUP, similarly to the ATM switching systems 102 and 103.
(S5) The ATM switching systems 103 and 102 which receive the response by the message CONNECT from the AES 104 respectively transfer the message CONNECT to the AES 101.
(S6) When the AES 101 receives the message CONNECT, the AES 101 judges that the connection to the AES 104 is set, and uses the allocated connection identifier to start transmission of ATM cells generated from the frame received from the LAN.
In FIG. 1, only the message SETUP and the message CONNECT are used for the sake of convenience. Actually, however, other messages are also used, such as a response confirmation message which indicates that the message transmitted from the transmitting side AES 101 is received by the receiving side AES 104.
Next, a description will be given of the procedure for a case where the connection is rejected by the receiving side AES when the connection establishment of the point-to-point communication is requested using the above described procedure, that is, when the connection establishment fails, by referring to FIG. 2. In FIG. 2, those parts which are the same as those corresponding parts in FIG. 1 are designated by the same reference numerals, and a description thereof will be omitted. This procedure is realized by the following steps (ST1) through (ST6).
(ST1) The AES 101 transmits a message SETUP to the ATM switching system 102 via the UNI A.
(ST2) The ATM switching system 102 which receives the message SETUP from the UNI A reserves a connection identifier (VPI or VCI) used in the UNI A if the ATM switching system 102 can accept the message SETUP, that is, if the ATM switching system 102 can provide the conditions included in the message SETUP. A connect message CONNECT is used to notify the connection identifier to the AES 101. In addition, the ATM switching system 102 transfers the message SETUP to the adjacent ATM switching system 103 via the NNI.
(ST3) The ATM switching system 103 which receives the message SETUP from the ATM switching system 102 allocates a connection identifier used in the UNI B and transmits the message SETUP including this connection identifier to the AES 104 if the ATM switching system 103 can accept the message SETUP, similarly to the ATM switching system 102.
(ST4) The AES 104 which receives the message SETUP from the ATM switching system 103 responds by a release complete message REL COMP with respect to the AES 101 if an information element which cannot be recognized is included in the message SETUP, a required information element is not included in the message SETUP or, it is judged that the conditions such as the requested band cannot be provided.
(ST5) The ATM switching systems 103 and 102 which receive the message REL COMP respectively transfer the message REL COMP to the AES 101, and release the connection identifiers allocated to the corresponding UNIs A and B.
(ST6) When the AES 101 receives the message REL COMP, the AES 101 notifies the user or application of a host that the setting of the connection failed. The operation thereafter follows the judgement of the user or application, and if a re-connect request or a re-transmit request is made, a new message SETUP is transmitted. In this case, however, a reference which is used to judge whether or not to change the contents of the message SETUP is not yet established at the present.
In FIG. 2, only the message SETUP, the message CONNECT and the message REL COMP are used for the sake of convenience. Actually, however, other messages are also used, such as the response confirmation message which indicates that the message transmitted from the transmitting side AES 101 is received by the receiving side AES 104. In addition, t in FIG. 2 indicates a time it takes for the AES 101 to transmit the data from the time when the AES 101 receives the frame (data) from the LAN.
A connection request from the transmitting side end system may be rejected because the connection cannot be guaranteed by the network or the receiving side end system. In this case, the rejection is made as a result of a negotiation which is made in relation to the connection to be set, and this rejection is inevitable in order to establish a connection which can guarantee the required band or service. In order to cope with such a situation, measures which are devised to increase the connection probability are considered within the standard, by making it possible to make two band requests, one for a large band and another for a small band.
However, when the signaling protocol is revised and the information essential for the conventional message SETUP is deleted, it may be impossible to communicate between two end systems supporting different versions of the signaling protocol. For this reason, when the connection request from the transmitting side end system is rejected by the receiving side end system, there was a problem in that the connection must basically be abandoned.
On the other hand, even if the transmitting side end system supports all versions of the signaling protocol, there is no means of knowing the version of the signaling protocol that can be supported by the receiving side end system to which the connection is to be made. For this reason, depending on the result of the call setup request which is once made, it is necessary to make a re-connect request, and there was a problem in that it takes time to establish the connection. For example, in a system in which an apparatus provided with both a LAN interface and an ATM interface sets the SVC in response to the frame received from the LAN interface, the time it takes for the connection to be set greatly affects the end system in the LAN because the end system transmits the frame without being conscious of the existence of a connection in the ATM system.